The goal of this project is to determine if a correlation exists between levels of potential genetic repair and protective processes and the aging rate of the mammalian species. Work has continued on the superoxide dismutase (SOD) and guanylate cyclase specific activity studies using brain, liver and heart tissues of 2 rodent and 12 primate species. These species covered a maximum lifespan potential (MLP) range of 3.5 to 95 years. No correlation was found between the level of SOD specific activity and MLP. However, and excellent correlation was found between the ratio of SOD and specific metabolic rate with MLP. Preliminary data with catalase shows similar results. These results suggest that longer lived species have superior protection against oxygen toxicity. Measurement of guaylate cyclase (GC) specific activity for the same species indicates an inverse correlation with SOD specific activity. In view of the possible activation of GC by hydroxyl radicals, these results suggest that GC specific activity may be involved in governing the level of SOD specific activity and perhaps other intracellular free radical protective processes.